The group A streptococcus (GAS; Streptococcus pyogenes) is a major bacterial pathogen of humans, globally causing over 700,000,000 infections and more than 500,000 deaths each year. Prophages and prophage-like chromosomal islands are prominent genetic elements in GAS with multiple examples found in every published genome, and many are known to be vectors for virulence genes. The long-term goal of our laboratory is to understand the role that S. pyogenes chromosomal islands (SpyCI) play in regulating host gene expression and promoting cell survival. As we have shown in our previous studies, SpyCIM1 regulates the DNA mismatch repair (MMR) operon in M1 genome strain SF370 by altering between integrated and episomal forms in response to environmental signals. Our central hypothesis is that SpyCI acts as genetic regulator of MMR and other repair and survival mechanisms in GAS, protecting rapidly growing cells from unwanted mutations while allowing the accumulation of changes, some of which could be adaptive, when resources become limiting. Once the role of SpyCI as gene regulators is known, it will aid in devising new pharmacological strategies that may up- or down-regulate GAS genes so as to interfere with normal bacterial metabolism. Further, it may provide key insights into the evolution of new strains of GAS since MMR has been demonstrated to play a key role in controlling horizontal transfer. Therefore, to test our central hypothesis, the specific aims of this application are to: 1. Determine the differences in global gene expression between strains that differ solely by the presence or absence of SpyCI or one of the MMR operon genes (lmrP) under their control. 2. Characterize the molecular signals that regulate the integrative state of SpyCI, which causes the host cell to cycle between wild type and mutator phenotypes. The PI and his laboratory are well qualified to pursue these studies, having pioneered this field of study. The results of these studies are expected to have a positive impact, fundamentally advancing our knowledge of GAS gene regulation and evolution, and thus could lead ultimately to improved control and antimicrobial strategies. Relevance: Streptococcus pyogenes is an important cause of bacterial disease in humans. This research will determine the role of a bacterial virus in regulating a key DNA repair system. The results wil increase our understanding of evolution and gene regulation in these bacteria and thus aid in devising new antimicrobial strategies. Further, in keeping with the goals of AREA grants, we will continue to provide research opportunities for undergraduate, graduate, and professional students as we have over the previous funding periods of this research.